Large birefringence smectic-A liquid crystals for high contrast bistable displays

We developed two kinds of bistable smectic-A liquid crystal mixtures. Compared with traditional cyanobiphenyl and cyanoterphenyl derivatives, several changes have been made in molecular design: Isothiocyanato is used as a substitute for cyano to increase the optical anisotropy; fluoro groups are added on 3 and 5 positions of the isothiocyanato substituent terminal phenyl ring to increase both the dielectric anisotropy and eutectic property of the smectic mixture; derivatives of (4-isothiocyanatophenyl) pyridine are introduced to produce a wide smectic range. Thanks to above designs, the final smectic-A mixtures exhibit highly improved properties, such as higher contrast, lower operation voltages and wider temperature range. Based on the developed liquid crystals, electronic tags were also demonstrated, which exhibit reliable performance. This work reveals new insights for tailing liquid crystal molecules with bistability, which is extremely meaningful for the design and fabrication of green display devices.